1. Field of the Invention
This invention relates, in general, to power line carrier communication systems and, more specifically, to distribution network power line communication systems for performing distribution automation functions.
2. Description of the Prior Art
Considerable effort has been devoted in recent years to develop distribution network carrier communication systems due to the increased desirability of performing certain distribution automation functions, such as automatic reading of utility meters, selective load control, performing load continuity checks, and the like. However, using the distribution network as a communication link presents several problems not encountered in existing high voltage transmission line communication systems. The distribution line, along with the large number of distribution transformers attached thereto, presents poor high frequency impedance characteristics which rapidly attenuate the communication signals, as well as introducing electrical noise and signal interference.
U.S. Pat. Nos. 3,967,264, 3,942,168 and application Ser. No. 649,774, filed Jan. 16, 1976, now U.S. Pat. No. 4,016,429, all assigned to the assignee of the present application, disclose some form of communication system via the distribution network of an electrical utility. In application Ser. No. 649,774, now U.S. Pat. No. 4,016,429, there is disclosed a communication system which uses the grounded neutral conductor of the power system and the real or ground return path to transmit carrier communication signals between a central communication terminal and remote communication terminals located on the premises of the utility company customers. U.S. Pat. No. 3,967,264, meanwhile, utilizes the primary and secondary conductors of the power system to transmit the carrier communication signals. In an effort to reduce the attenuation and improve the transmission of the communication signals over the distribution network power conductors, these communication systems utilize signal repeaters which amplify the communication signal and improve its signal to noise ratio.
In the carrier communication system disclosed in U.S. Pat. No. 3,942,168, signal repeaters are disposed in signal communication with both the primary and secondary distribution network power line conductors at each distribution transformer site. In this system, the repeater, in addition to amplifying a signal, provides a bypass circuit for the interrogation and response signals around the associated distribution transformer which presents a significant attenuation at the frequencies of the communication signals, especially in the direction from the primary to secondary winding. The repeaters also include means for delaying a received signal, with the delay time interval selected such that the amplified signal is not applied to the power line at the same time the repeater is to receive another signal. This is implemented by means of a switch which connects either the receiver or the transmitter to the conductor. Each repeater includes two channels, each comprised of a receiver, logic and transmitter sections, for handling the bidirectional flow of interrogation and response signals between the central communication terminal and the remote communication terminals at the customer premises.
Similarly, signal repeaters are utilized at each distribution transformer in the communication system disclosed in U.S. Pat. No. 3,967,264 to provide a bypass circuit for the interrogation signals around the primary of the associated distribution transformer. Each repeater also includes two channels, each comprised of a receiver and transmitter section, to provide two-way communication signal transmission between the central communication terminal and the remote communication terminals. In addition, each repeater and remote communication terminal is uniquely addressable, thereby allowing the central communication terminal to communicate exclusively with a selected repeater and one of its associated remote communication terminals.
Although these types of distribution network communication systems are satisfactory in operation, the necessity of bypassing the primary of each distribution transformer results in the use of a large number of signal repeaters. Furthermore, each repeater must contain two separate channels to enable it to handle the bidirectional flow of interrogation and response signals.
Thus, it would be desirable to provide a distribution network communication system which has improved carrier communication signal transmission characteristics over prior art distribution network communication systems. It would also be desirable to provide an improved signal repeater which has extended range capabilities thereby allowing fewer repeaters to be used throughout the distribution network. Furthermore, a simplified repeater construction wherein one receiver and one transmitter are utilized to handle both the interrogation and response communication signals would also be desirable.